Thank you for the detailed explanation.
These advice is very helpful for me.
When I would like to announce MOD using someone's codes, I send e-mail and get permission.
And I write "I copied someone's codes" to a Readme file.
If I cannot get use permission of a code from the original MOD author, I do not announce custom MOD.
However, one question still remains.
The case where there is no reply from the author, or when I cannot contact the author,
Am I able to announce custom MOD?

If this question does not have a general answer, I would also welcome personal opinion.
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